Two types of photovoltaic energy conversion technologies are in use today. One is in the form of panels, comprising of wafers of a semiconductor material that contain cells linked together to produce a unit whose size can be as large as 99 cm by 195 cm in commercial grade panels. In these types of panels, the semiconductor material that converts light to electricity is sandwiched between a structural aluminum backing material, and a top glazing from which the light (solar radiation) is incident. Silicon is the dominant semiconductor material in panels of this kind. Light incident on such panels can be from any angle; i.e., they can accept diffuse light.
The second type of photovoltaic technology uses collection optics to gather and concentrate light onto small areas of semiconductor where light-sensitive cells are fabricated. This is the basis of concentrated photovoltaic (CPV) technology, where compound semiconductor thin films synthesized from group III-V compounds are used for the light-sensitive cells. Two of its main virtues are that it uses less semiconductor material and yet has a much higher conversion efficiency of >40% in research-grade multi-junction cells, compared to a typical conversion efficiency of 18-25% for silicon panels. Concentrated photovoltaic modules accept normal incidence light, and are typically provisioned with a tracking system that keeps the modules optimally aligned to the sun to consistently produce the most energy on any typical day. Unlike flat plate silicon panels, light collection optics are integrated onto CPV modules. Because of the high concentration of light incident on a cell module, there is a need to uniformly distribute incident light over the area of the solar cell chip. Such areas can range from a few square millimeters to several tens of square centimeters. Distributing light uniformly over these areas is necessary because it avoids the onset of hot or cold spots that could damage a chip. This is particularly important for large area chips (>25 mm2). The usual approach to distributing light over CPV cells is to use a truncated pyramidal glass prism that is attached (with an index-matching epoxy) to the cell. Light incident on the large surface of the prism is guided along the length of the prism by total internal reflections and emerges scrambled at the bottom of the prism, where it is attached to a solar cell. Properly dimensioned prisms can often achieve uniform light distribution over the surface of a solar cell. However, a number of issues have dogged this approach. Among them is the fact that the multiple surfaces and interfaces of the prism can cause cumulative light loses that can be significant. The second other major issue is delamination of the prisms from cells due to temperature variations. A third problem is connected to the manufacture of the prisms. Most are manufactured manually, resulting in a time consuming and costly process. Nevertheless, the inventor recognizes that CPV technology has potential for scalability in constructing large-scale power plants at low cost, if the above problems could be solved.